Hi all,
I'm a homeowner in Louisville, Colorado who contracted with a local driller in 2008 to have four 200-foot geothermal loops installed in my backyard to feed a hydronic heat pump. I'm looking for hardware/software recommendations on how to measure the temperature at various depths of my geothermal loop.

During the loop installation process, I prepared four thermistors with long cables and homemade junction waterproofing for attachment and installation into one of these vertical loops. The contractor attached them to the loop at various depths (5, 8, 60, 100, and 200 feet). The bore passed through some clay soil, shale, and coal to get to this final depth, and passed through the water table (at the time). I believe the bore backfill was with a bentonite mixture.

I've had but never had the time to figure out a good solution to hook up the wires to a monitoring system, so have had eight wires (two per thermistor) hanging out of my basement wall for the last 11 years. I need to double check, but believe that the thermistors are 10 kohm nominal values, and were made by Measurement Specialties (now apparently owned by TE connectivity). I probably bought the 44036RC model, which has the best tolerance.

I have a Linux-based server running at my home, and ideally I would run some monitoring application that I could install there and easily check on the temperature status of the loop. I do not have any hardware implemented to read the thermistor. Typically to measure the thermistors' resistance, the thermistors are incorporated with other resistors and a voltage bias, then read with an analog-to-digital chip that is read by software.

Does anyone have a recommendation for thermistor-reading hardware and software that is readily available, and affordable for a backyard geothermal homeowner like myself? I can imaging that there might exist some hardware running on Arduino or Raspberry Pi somewhere out there, but I don't know where to start to look for that. I'm short on time with several young kids at home, so can't even begin to envision taking on such a project myself at this time.

I’ve been researching the same concept to monitor thermistors, current sensors and differential pressure sensors for my build.

What I’ve come up with so far:

Convert the thermistors to an analog 4 to 20 ma signal using a thermistor transmitter module.

Then convert the 4 to 20 ma analog signal to a digital output that can be transferred to a PC or read directly via the cloud. Many options, here is a product family that I’ve used before and is highly reliable.

I had a look at the X-418, and that looks like a great solution for what I need. I will likely just bypass the 4-20 mA approach, though, as the X-418 appears to be able to ingest regular DC voltages directly, which is what my thermistor/resistor network will generate. I like that the X-418 is configurable to send on data out its Ethernet port - I can have that sent to my home server.

Also, I had forgotten to mention that my Linux-based server is made by Synology, and there are a number of applications that have been created that can run on it. On this machine I envision to (1) have a database of collected data, and (2) a means to display selections from that database. It seems that a MySQL database would be a standard way to satisfy (1). For satisfying (2), one forum elsewhere had suggested Home Assistant running on Synology, and another suggested using pChart. Also there apparently is a Google tool called Google Chart Tools, though I'm not sure if that would run on the Synology box per se.

Given that I've not implemented anything as ambitious as the software I've described above, I'm still interested in hearing ideas from anyone about a software solution, or even suggestions of details to implement the above software ideas.

This is what I have used for my HVAC automation at home. I actually use two of them that have their modbus registers read by a raspberry Pi using Collectd and Collectd GraphPanel to display as a web page from the PI. You can download the software and experiment without actually buying a device. It is nice programming interface. Like a ladder diagram, but easier and powerful.

The MBus_io12_LCD is DataNab's newest programmable I/O module. It is a professional grade automation device loaded with features and perfect for almost any control or monitoring application. The MBus_io12_LCD communicates using the Modbus-RTU protocol over RS485 networks.

Interesting that you have the sensors in the ground and never tempted to connect them to a reader, but I know how thus things sometimes go. I hope you can work this out and since you have 2 wires for each sensor, it should not be to difficult.

I will keep an eye on your post and hope to find some info for my plan below and hope you get this all rigged-up.

Please let me know if I am hijacking your thread and I will delete the below and setup my own thread for it, but it fits in the same bracket so to speak.

For the specialists here, I am trying to set something up like Sean did 11 years ago and 'wing' has comment on my attempt to do what is not sensible at a different point but that is an other issue. My plan is to attache ten Dallas DS18B20 to a cable every 10m (33'), set all the reading hard & software up to make sure all works, pull fitting heat shrink over each sensor, seal with silicon and then shrink before the silicon is hardened and pull a second heat shrink tube over the 100m, seal both ends and shrink . The coast would be minimal, I figure about $100 is plenty for the cable and may include the Arduino. To be triple save, one could insert this sensor cable into 3/8 or 1/2' poly pipe and seal. Reading would probably be once per week or what ever is needed.

The cable would go to my heat control room and could go to my networking hub.

Having 35 years in the automation business has sparked my attention with your interesting thread.

Specifically the idea of digital transmitters in the automation world is somewhat unconventional. That being said, I have reviewed the specs on the bus-rated Dallas sensors and can appreciate the simplicity that they offer from a wiring perspective.

JoergK, I would pursue your idea, and install into a PVC pipe, and seal the joints liberally with silicone. I would obviously dry-test your communications and verify that all sensors (nodes) are configured and operational prior to wet insertion.

Seems like the collection of the information is more of the issue. I am a PLC/SCADA developer - electrician and have integrated systems similar to what you have talked about - only using more conventional 4-20mA loops - where HART and under/overrange can be monitored more accurately.

I am familiar with Raspberry Pi, and the simplicity of some of the freeware aps that are out there. Personally, I would stick to Dallas's monitoring system if given the option - unless the communication protocol can be deciphered easily.

Enjoy your project - seems like something that we could bring to market.

A friend has a 13 well installation for several systems [two air-handlers, one w-w for floors and a pool, two w-w for domestic water.] We were curious about the balance between the wells. So we put One-Wire system DS18B20 probes against each well return and one on the source. We will use an Embedded Data System unit to make the data available via the EDS webserver on the house LAN.

We actually put two One-Wire sensors at each location: a good one from EDS and a really cheap one from Amazon. They are on different pairs. This because we worried about failures and major effort to ever replace same.

If you use One-Wire, I recommend you carry the power out to each. (So it's really Three-Wire;=.) That assures better performance with many devices on a loop.

On the sensor-pipe coupling, we had no off-the-shelf solution so we kludged. We tiewrapped them to the well legs, then taped them, then all inside a split Sonotube. The common one was just a box from a noted Seattle maker/shipper of boxes. Then we filled the tube and box with insulating foam.